The present invention relates to high speed generators and, more particularly, to the structure of the rotors of such generators.
Generator systems that are installed in aircraft may include three separate brushless generators, namely, a permanent magnet generator (PMG), an exciter, and a main generator. The PMG includes permanent magnets on its rotor. When the PMG rotates, AC currents are induced in stator windings of the PMG. These AC currents are typically fed to a regulator or a control device, which in turn outputs a DC current. This DC current next is provided to stator windings of the exciter. As the rotor of the exciter rotates, three phases of AC current are typically induced in the rotor windings. Rectifier circuits that rotate with the rotor of the exciter rectify this three-phase AC current, and the resulting DC currents are provided to the rotor windings of the main generator. Finally, as the rotor of the main generator rotates, three phases of AC current are typically induced in its stator windings, and this three-phase AC output can then be provided to a load such as, for example, electrical aircraft systems.
Among the important components in such generator systems are the rotors of the exciters. Conventional exciter rotors are formed from multiple laminations that are thin plates that are stacked axially along the generator shaft. The rotors often have many (e.g., more than eight) poles, and also support the rectifier circuits that convert the AC power generated in the rotor windings into the DC power that is to be provided to the main generator rotor.
Such conventional exciter rotors have several limitations. Because the generators installed in aircraft will often be variable frequency generators that rotate in the speed range of 12,000 rpm to 24,000 rpm, large centrifugal forces are imposed upon the rotors of the generators. Because the structure of the rotor includes multiple laminations, and because the laminations often are made from materials that are limited in their strength, imbalances in the rotor can occur when changes or shifts in the laminations affect the relative alignment of the laminations with one another or with respect to the generator shaft. Additional imbalances can occur when shifting or other changes in the positioning of the laminations affect the positioning of the many wire windings or rectifier circuits being supported by the laminations. Such imbalances can create inefficiencies in the operation of the generators or risk potential failures.
Additionally, the use of laminations in the exciter rotors makes it difficult to accurately and consistently manufacture such rotors. Slight variations in the thicknesses of the laminations of the exciter rotor can make it difficult to predictably manufacture exciter rotors having a given overall axial thickness. Further, the complicated shape of the laminations, with their many radially protruding pole extensions and deep radial cut-outs, often renders it difficult to manufacture and assemble the laminations.
Hence, there is a need for a new exciter rotor assembly that is reliable, robust and can be easily manufactured within tolerances both in terms of the shape of the outer perimeter of the rotor and the axial thickness of the rotor. Additionally, there is a need for a new exciter rotor assembly that is capable of maintaining proper balance when operating at high speeds even though it includes multiple laminations and supports many wire windings and rectifier circuits.
The present inventors have recognized that a new exciter rotor assembly can be developed that includes a hub that is supported by the generator shaft and in turn supports narrow ring-type laminations around its outer perimeter. The laminations are shrunk fit onto the hub, which is made from a strong material, is carefully manufactured to have a particular axial thickness, and in turn is shrunk fit onto the generator shaft. By incorporating such a hub in between the narrow ring-type laminations and the generator shaft, the radial width of the laminations is significantly reduced and the above-described problems associated with the manufacture and use of the laminations are alleviated.
In particular, the present invention relates to a rotor that includes a hub configured to be supported by a shaft that extends along an axis, a plurality of laminations, and a plurality of wire windings supported by the plurality of laminations. The hub includes an inner structure configured to support the hub relative to the shaft, an outer structure, and an intermediate structure that is coupled to the inner and outer structures and supports the inner and outer structures relative to one another. The plurality of laminations are supported by the outer structure.
The present invention further relates to a generator that includes a stator, a shaft, and a rotor supported by the shaft. The rotor includes a plurality of laminations, a plurality of wire windings wrapped around the plurality of laminations, and a means for supporting the laminations relative to the shaft. The means for supporting has a first radial width extending from the shaft to the laminations that is larger than a second radial width of the laminations that extends from the means for supporting to an outer circumference of the rotor.
The present invention also relates to a hub for implementation in a high-speed generator rotor, where the hub includes an inner structure configured to support the hub relative to a shaft, an outer structure configured to support a plurality of laminations, and an intermediate structure that is coupled to the inner and outer structures and supports the inner and outer structures relative to one another. The intermediate structure defines a plurality of cavities within the hub.
The present invention additionally relates to a method of constructing a rotor. The method includes providing a hub having an outer structure with a cylindrical support surface and a retaining ring, an inner structure forming a cylindrical cavity, and an intermediate structure coupled to the inner and outer structures and configured to support the inner and outer structures relative to one another. The method further includes positioning a plurality of ring-type laminations and a pair of insulating rings onto the cylindrical support surface. A first of the pair of insulating rings is positioned on a first side of the plurality of laminations and a second of the pair of insulating rings is positioned on a second side of the plurality of laminations. The laminations and insulating rings are positioned so that the first of the pair of insulating rings abuts the retaining ring. The method additionally includes shrink-fitting the ring-type laminations and insulating rings onto the cylindrical support surface, positioning a balancing ring onto the cylindrical supports surface so that the balancing ring abuts the second of the pair of insulating rings, shrink-fitting the balancing ring onto the cylindrical support surface, and wrapping a plurality of wire windings onto the laminations.
Other features and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.